Free Living Amoeba

Question 1

The dividing form of Naegleria is……, it moves by…..

Answer 1

Amoeboid trophozoite
Broad pseudopodium (lobopodia)

Question 2

When is flagellated form present? Why

Answer 2

When amoeboid is exposed to change in water ionization & when food is scarce, as it is rapidly motile thus moves rapidly searching for food.

Question 3

GR: Cyst form of Naegleria is not seen in clinical specimens

Answer 3

Because the course of disease is so rapid & fatal before the trophozoite can encyst

Question 4

Mode of infection of Naeglaria

Answer 4

By swimming or diving in contaminated water by amoeboid trophozoite (infective stage), rarely by inhalation of aerosols containing parasites

Question 5

Describe the mechanism of each with respiect Naegleria
1. Invasion
2. Nerve injury

Answer 5

1.Penetrate nasal mucosa, migrate via olfactory nerve, ciribriform plate to enter meninges, where they muliply in the peri-vascular spaces causing suppurative meningoencephalitis
2. Trogocytosis, ingestion of cytoplasm through feeding cup + contact dependent lysis (also in acanthamoeba)

Question 6

Incubation period & prognosis of Naegleriaz

Answer 6

2-5 days
Very poor, most cases are fatal

Question 7

Distinguishing clinical feature of amoebic meningits

Answer 7

Change of taste & smell

Question 8

Microscopic exam of CSF in Naegleria shows…..

Answer 8

Inc PMNs & lymphocytes

Question 9

Dsecribe treatment of Naegleria

Answer 9

Amphtericin B slow IV infusion in a dose of 1mg/kg/day for 9 days & 1mg intrathecally on alternate days until CSF is clear.

Question 10

Mention preventive measures for Naegleria

Answer 10

1. Avoidance of contact with contaminated water
2. 20% biguanides (Baguacil) directed to swimming pools
   Chlorination is not protective

Question 11

Mention conditions that cause Acanthamoeba encystation

Answer 11

Deprivation, desiccation & changes in temp & pH

Question 12

Mode of infection of Anabthamoeba

Answer 12

1. Inhalation of trophozoite or cyst through nasal passages & lung
2. Entrance through skin lesion or genitourinary tract
3. Through corneal abrsaions esp with contact lenses

Question 13

……occurs in immunosuppressed patients while……occurs in healthy individuals

Answer 13

Granulomatous amoebic encephalitis
Amoebic keratitis & corneal ulcer

Question 14

C/P of amoebic keratitis

Answer 14

Chronic progressive ulcerative disease of the eye
Painful ulcer of the cornea, congested conjunctiva, complete corneal opacity, blindness
Disease is increasing with frequent use of contact lenses

Question 15

Diagnostic stage of Naegleria is….., while that of Acanthamoeba is…..

Answer 15

Amoeboid trophozoite
Trophozoite or cyst

Question 16

Most reliable diagnostic method for GAE is….

Answer 16

Brain biopsy

Question 17

Describe treatment of each of the following
1. GAE
2. Amoebic keratitis

Answer 17

1. Sulfadiazine +ketoconazole or fluconazole +pentamidine+flucytosine
2. Tropical chlorhexidine and polyhexamethylene bigyanide either alone or combination? If epithelium alone is involved debridement may be sufficient. Penetrating keratoplasty may be necessary if non-respondant to medical treatment.